The present invention relates to a novel inductive thin-film magnetic head for a dual-element thin-film magnetic head unit including an inductive thin-film magnetic recording head and a magnetoresistive reading head.
With the recording density of a magnetic disk apparatus ever on the increase, magnetic coercive force of the magnetic recording medium is increased while the track width of the inductive thin film magnetic head used for recording is decreasing. Also, the downsizing of the magnetic disk apparatus has reduced the reproduction output of the inductive thin-film magnetic head. For this reason, an inductive thin-film magnetic head is used as a recording head, and a magnetoresistive head is used for converting the leakage magnetic field from the medium as a resistance change. The magneto-resistive head includes a sensor constituted of a magnetoresistive element, a giant magnetoresistive element, a ferromagnetic tunnel junction element, etc., and one of the magnetic shields for improving the spatial resolution is shared with one of the magnetic cores of the inductive thin-film magnetic head.
The current trend of the shape of the magnetic core along the air-bearing surface of an inductive thin-film magnetic head is such that the width of the upper magnetic core determines the track width and the width of the lower magnetic core serving also as the upper shield film of the reproductive head is several tens of times larger than the track width. With the decrease in track width, however, the magnetic field expanding out of the track ends has become conspicuous.
In order to solve this problem, the structure of an inductive thin-film magnetic head with the upper portion of the lower magnetic core of the inductive thin-film magnetic head is shaped to the same width as the upper magnetic core is described in U.S. Pat. No. 5,438,747. Also, the structure of the inductive thin-film magnetic head having a trench including a pole tip layer with the width thereof defining the track width is described in JP-A-7-296328 laid open Nov. 10, 1995 and corresponding to the U.S. patent application Ser. No. 229,484 filed Apr. 19, 1994.
The inductive thin-film magnetic head described in U.S. Pat. No. 5,438,747 (JP-A-7-262519) and JP-A-7-296328 has a protrusion structure having substantially the same width as the track in the neighborhood of the air-bearing surface in the upper portion of the lower magnetic core. This protrusion structure facilitates the machining of the track to a width in the order of submicrons, and the magnetic fields are concentrated in the protrusion structure.
The prior art described above may develop a magnetic domain wall in the corners of the magnetic material. In the case where the lower magnetic core of the inductive thin-film magnetic head doubles as the upper magnetic shield of the reproductive head, therefore, a domain wall may occur in the portion of the upper magnetic shield extending from the end of protrusion structure to the neighborhood of the sensor portion of the reproductive head. This domain wall is moved by the leakage magnetic field from the medium or the change in the external magnetic field, thereby posing the problem of output changes.
Accordingly, the object of the present invention is to provide a dual-element thin-film magnetic head with small fluctuations of the reproduction output and small reproduction noises.
According to one aspect of the invention, there is provided an inductive thin-film magnetic head comprising a lower magnetic core formed on a substrate, an upper magnetic core arranged in opposed relation to the lower magnetic core with a magnetic gap film therebetween, a coil interposed between the lower magnetic core and the upper magnetic core, and a dielectric layer for insulating the lower magnetic core, the upper magnetic core and the coil from each other, wherein the forward ends of the lower magnetic core and the upper magnetic core have the same width as the track, and the rear ends of the lower magnetic core and the upper magnetic core have a width larger than the width of the forward ends thereof.
According to another aspect of the invention, there is provided an inductive thin-film magnetic head, wherein the lower magnetic core preferably is formed of at least two magnetic layers with a non-magnetic layer therebetween and the forward end of each of the magnetic layers in contact with a magnetic gap has the same width as track.
According to an embodiment of the invention, an inductive thin-film magnetic head comprises a lower magnetic core formed on a substrate, an upper magnetic core having its forward end thereof coupled to the lower magnetic core through a magnetic gap film and its rear end thereof coupled to the lower magnetic core, the forward end being smaller in width than the rear end thereof, the width being made progressively smaller from the rear end toward the forward end thereof, a coil arranged to surround the upper magnetic core and the lower magnetic core, and a dielectric layer formed between the coil, the upper magnetic core and the lower magnetic core, wherein a protrusion structure having the same width as the track is formed at least on the portion of the lower magnetic core in the neighborhood of the air-bearing surface and a non-magnetic layer is formed at least in the neighborhood of the air-bearing surface between the lower magnetic core and the protrusion structure.
Preferably, the thickness of the non-magnetic layer between the lower magnetic core and the protrusion structure is smaller than the thickness of the magnetic gap film, and the saturation magnetic flux density of the protrusion structure is not less than 1.3 T.
According to another embodiment of the invention, the non-magnetic film is held between the lower magnetic core and the protrusion structure formed on the lower magnetic core of an inductive thin-film magnetic head. In this way, the magnetic coupling between the lower magnetic core and the protrusion structure is reduced in order that no domain wall is formed in the neighborhood of the sensor of the reproductive head. The output fluctuations and noises of the reproductive head which otherwise might be caused by the generation, extinction and relocation of the domain wall can be reduced.
The non-magnetic film between the lower magnetic core and the protrusion structure of the inductive thin-film magnetic head should be sufficiently thin to reduce the magnetic coupling between them to such an extent as not to form any domain wall in the neighborhood of the sensor of the reproductive head of the lower magnetic core. In the case where the non-magnetic film is thicker than the gap film, the non-magnetic film would function also as a gap, with a result that the recording magnetic field would be made wider with its intensity being made correspondingly smaller.